During the production of fibers for papermaking, wood or other fiber source is ground into chips and/or mechanically treated such that the chips may be broken down further and refined into individual fibers.
Disc refiners are used with high density stock containing forty to sixty percent fiber by weight. The disc refiner acts to break down clumps of fibers into individual fibers. Disc refiners are also used with low density, low consistency pulp of two to five percent fiber dry weight. In such applications the disc action increases the freeness or bonding capability of the individual fibers.
A refiner disc consists of a disc-shaped steel or steel-alloy casting which has a multiplicity of generally radially extending bars integrally cast to extend from the surface of the disc. A first refiner disc is mounted on a rotor for rotation and another disc is held opposed to the first refiner disc, either by rigid mounting or by mounting on an opposite rotating rotor. The refiner discs, as they move past each other, separate and refine the wood pulp as it passes between the opposed discs.
When dealing with high consistency pulp and wood chips, the edges of the refiner bar act as cutting edges for separating fibers from wood chips or clumps of fibers. The edges of the bars are formed by casting the bars integrally with the refiner discs and grinding the as-cast disc parallel to the disc surface, thus creating sharp edges between the ground surface and the sides of the refining disc bars.
One problem that arises in the use of refiner discs is that wear of the cutting edges causes the refiner discs to loose effectiveness over time.
U.S. Pat. No. 5,165,592 to Wasikowski, which is incorporated herein by reference, teaches a method of preferentially hardening the sides of the bars on a refiner disc. This hardening of the bar sides results in the bar sides wearing less rapidly than the central top surface of the bars. This wearing effect has the result that the bars tend to wear sharp, rather than dull.
The tendency of refiner discs to become worn and less effective, and thus require replacement, is a major cost component in the use of refiners.
Refiner discs are needed which have improved wearability and hence longer life between replacement and shutdown of the apparatus.